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Psysical, Osi Model, (N-1)-PCI added at layer N, PCI - Coggle Diagram
Psysical
eth
UTP
unshielded up to 6
FTP
folied
STP
shielded from 6a
8 wires
coax
2 wires
shield second wire
Expensive and not easy to bind
obsolete for LANs
Optic fiber
glass based
Core + cladding
different reflective coefficient
adv
Low attenuation
high bit rate
disadv
difficult to bind
expensive
only for point to point
Digital modulation
analog signal representing digital
modulating signal
multiplied to sin
Depending on phase
ASK
FSK
PSK
QAM
number of symbols
Radio
Fading and shadowing
Coding (V level based)
Unipolar
0v -> 0
sync loss
difficult to put 0V
Polar
NRZ
11 -> no down transition
RZ
11 ->Transition to zero
Biphase
eg. manchester
2 voltages with different polarities
Bipolar
0v -> 0
-V or V -> 1
Ternary simbols enabled
nBmB
symbol m->n(data) with n<m
easy sync not too 0 or 1
control info (extra)
Osi Model
Layers
Entities
protocols at same layer
service at Layer n-1 connects users at layer n
Connection between SAPs at same layer
Specific access point
PDU
PCI
SDU
At layer N, N-SDU
N-1-PDU
Not modified in lower layers
On reverse They are peeled offf
concatenation
Segmentation
payload of upper layer to big so divide it in chunks
SDU divided in many PDU
PDU in many (N-1)SDUs
Data link
flow control
speed
based on receiver load
faults
correction codes
queeing
Intermediary nodes errors correction
Network
network topology
Rounting
Pricing
Connection
Congestion control
based on all network load
(N-1)-PCI added at layer N
PCI
ARQ
Types of aknowledgement (unidirectional approach)
Stop and wait
Transmitter
Copy and send
timer based
time is a critical choice
resend when no ack
receiver sends ACK
Check PDU correctness
check Id
Rx sends next expected packet number
PDUs number is mandatory
One packet per cycle (RTT)
Time wasted during wait
On errors
Packet duplication
Wrong number id
Ack not received
Send ack again
Packet Lost
Time out expires
Packet sent again
Non sequential cannel (one bit id)
if first ack Delayed and second packet lost
third packet discarded
Rx discards the wrong packet
One packet lost, one discarded
Tx not aware of issues
two bits id
rx continues to ask for before packet
close connection
Life time of PDU ACK
first ack arrives in fifth packet sent
go back
Tx window
Max PDUs sent without ACK
Based on mem and trade off
W t
Wr different means error
bigger -> more efficient
max size Wt < 2^k
k seq number
replica could be accepted as new packet
Selective repeat
Wr not size 1
memory at receiver
usually Wr = Wt
Wt + Wr < 2^k
k = bit for ack
selective ack
accumulative ack
up to which point reception was ok
repeats all non received PDUs
not in sequence -> stored
if in Wr
in sequence -> passed to higher layer
useless if less than 1 lost packet
Errors
replica interpreted as new and stored
real new one discarded
Throughput
min(Wt/RTT , link_speed)
optimal Wt to RTT chosen
RTT based on net congestion
Data
Parity bit
next packet number
Addresses
Error
Flow
Sequence
ACK (wait for confirm)